The present invention relates to a new and improved construction of measurement apparatus for determining the degree of filling of a casting mold -- also conveniently simply referred to as a mold --, having mold halves or parts which are supported against one another, against the action of a molding mass or material filled under pressure into a molding compartment or cavity of the mold, by means of a displacement device embodying a closure device comprising a closure cylinder and a closure piston.
It is already known to the art in the case of injection molding machines for processing plastic materials which can be plasticized, to automatically regulate parameters influencing the degree of filling of the mold, such as for instance the injection pressure, the after-pressure, the dosing volume or the setting time of the injected material, as a function of the relative movement occurring between the two mold halves which is in the sense of opening the mold due to the action of the pressure of the injected mass of material during the injection molding operation. It has already been proposed to arrange measurement or measuring devices at the mold, which devices sense the changes in shape or position of the mold brought about by the pressure of the injection molding material in the form of a signal value or amplitude. Measuring devices of this type are associated with a number of different drawbacks. What should be readily apparent is especially the disadvantage that each time the mold must be replaced it is equally necessary to exchange the measurement device together with the mold, and thus, sensitive components of such measurement device are exposed to the danger of damage. There can be however also provided for each mold a separate measurement device, but such is associated with considerable additional costs.
Furthermore, it has been found in the case of measurement devices which are arranged at the mold the measurement operation is exposed to disturbance factors which falsify the measurement result and lead to disturbances in the regulating function. Thus, for instance, the measurement operation can be influenced by the thermal energy transmitted from the heated mold to the measurement device.
Disturbance factors also have been then ascertained when the measurement device is arranged at one of both mold clamping or mounting plates because the bending-through of such mold mounting plates -- and which bending-through arises under the action of the closing pressure of the mold -- influences the measurement result.